Method of sealing an epitaxial silicon layer on a substrate

ABSTRACT

According to one aspect of the invention, a method of processing a wafer is provided. The wafer is located in a wafer processing chamber of a system for processing a wafer. A silicon layer is then formed on the wafer while the wafer is located in the wafer processing chamber. The wafer is then transferred from the wafer processing chamber to a loadlock chamber of the system. Communication between the processing chamber and the loadlock chamber is closed off. The wafer is then exposed to ozone gas while located in the loadlock chamber, whereafter the wafer is removed from the loadlock chamber out of the system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of and a system for sealing anepitaxial silicon layer formed on a semiconductor wafer.

2. Discussion of Related Art

Integrated circuits are formed in and on silicon and other semiconductorwafers. Wafers are made by extruding an ingot from a silicon bath andsawing the ingot into multiple wafers. In the case of silicon, thematerial of the wafers is monocrystalline. An epitaxial silicon layer isthen formed on the monocrystalline material of the wafer. The epitaxialsilicon layer is typically doped with boron and has a dopantconcentration of about 1×10¹⁶ atoms per centimeter cube. A typicalepitaxial silicon layer is about five microns thick. The material of theepitaxial silicon layer has better controlled properties than themonocrystalline silicon for purposes of forming semiconductor devicestherein and thereon.

Once the epitaxial silicon layer is formed, the wafer is removed fromthe wafer processing chamber and exposed to ambient air. The airoxidizes the exposed epitaxial silicon layer to form a native oxidelayer thereon. The epitaxial silicon layer and the native oxide layerare exposed to contaminants in the air and are usually filled withimpurities and particles. When semiconductor devices are formed on asurface which is filled with impurities, the electronic devices oftenfail.

It has been suggested that exposure of an epitaxial silicon layer toozone gas will provide an efficient process for forming a very pureoxide layer on the epitaxial silicon layer.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method of processing a waferis provided. The wafer is located in a wafer processing chamber of asystem for processing a wafer. An epitaxial silicon layer is then formedon the wafer while the wafer is located in the wafer processing chamber.The wafer is then transferred from the wafer processing chamber to aloadlock chamber of the system. Communication between the processingchamber and the loadlock chamber is closed off. The wafer is thenexposed to ozone gas while located in the loadlock chamber, whereafterthe wafer is removed from the loadlock chamber out of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference tothe accompanying drawings wherein:

FIG. 1 is a plan view of a system for processing a wafer;

FIG. 2 is a diagram of a loadlock assembly forming part of the systemand illustrates a loadlock chamber thereof in sectioned side view;

FIG. 3 is a flow chart of how the system is operated;

FIG. 4 is a time chart of how the system operates;

FIG. 5 is a cross-sectional side view of a wafer which is processedaccording to the invention;

FIG. 6 is a cross-sectional end view of an ozone generator which is usedin the loadlock assembly;

FIG. 7 is a cross-sectional side view of the ozone generator;

FIG. 8 is a graph of ozone concentration against backfill rate; and

FIG. 9 is a graph of oxide formation against ozone concentration.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method whereby an epitaxial siliconlayer formed on a silicon wafer is sealed with an oxide formed due toexposure to ozone gas. A plurality of the wafers are located in a batchin a loadlock chamber and exposed to ozone gas under controlledconditions. The ozone gas forms a stable and clean oxide layer on theepitaxial silicon layer of each wafer. The oxide layer can later beremoved to leave the epitaxial silicon layer exposed and containingsubstantially no impurities. There are certain advantages for processingthe wafers in the loadlock chamber. One advantage is that anotherchamber which is designated for a step in an existing process does nothave to be dedicated for exposing the wafers to ozone gas. Anotheradvantage is that such a system is relatively safe because there is asubstantially reduced likelihood that the ozone gas will mix withhydrogen gas within the system and cause an explosion, in particularbecause the pressure within the loadlock chamber is lower than a chamberin the system where hydrogen gas is used. The system is also safebecause the pressure within the loadlock chamber is always belowatmospheric pressure of an area around the loadlock chamber when ozonegas is within the loadlock chamber so that there is reduced likelihoodthat the ozone gas will escape to a surrounding area and cause anexplosion. Another advantage is that the overall time taken to processwafers is maintained.

FIG. 1 of the accompanying drawings illustrates a system 10 forprocessing a semiconductor wafer. The system 10 includes a factoryintegration unit 12, first and second batch loadlock assemblies 14A and14B, a transfer chamber 18, first, second, and third wafer processingchambers 20A, 20B, and 20C, and a cooldown chamber 22.

FIG. 2 illustrates one of the loadlock assemblies 14 in more detail. Theloadlock assembly 14 includes a loadlock chamber 24, a cassette elevator26, a wafer cassette 28, a pump 30, and apparatus 32 for supplyinggasses into the loadlock chamber 24.

The loadlock chamber 24 defines an enclosure 34 and has a door opening36 on one side thereof and a slitvalve opening 38 on an opposing sidethereof. The factory integration unit 12 mates with the loadlock chamber24 over the door opening 36. A door 40 is mounted to the loadlockchamber 24 for movement between a position as shown in FIG. 2 whereinthe door 40 closes the door opening 36, and a position wherein the dooropening 36 is open so that the confines of the factory integration unit12 are in communication with the enclosure 34.

The transfer chamber 18 mates with the loadlock chamber 24 over theslitvalve opening 38. A slitvalve 42 is mounted to the loadlock chamber24 for movement between a position as shown in FIG. 2 wherein theslitvalve 42 closes the slitvalve opening 38, and a position wherein theslitvalve opening 38 is open so that the enclosure 34 is incommunication with the confines of the transfer chamber 18.

The cassette elevator 26 includes a shaft 44 and a support plate 46. Theshaft 44 extends through an opening in a base of the loadlock chamber24. A seal (not shown) is located between the shaft 44 and the base ofthe loadlock chamber 24. The support plate 46 is secured to an upper endof the shaft 44.

The wafer cassette 28 includes a frame 48 with a plurality of fins 50located on the frame. The fins 50 are positioned relative to one anotherso as to be jointly capable of supporting a total of twenty-five wafersabove one another. The wafer cassette 28 is located on the support plate46. The wafer cassette 28 can be elevated by extending the shaft 44 intothe loadlock chamber 24, and lowered by retracting the shaft 44 from theloadlock chamber 24. By elevating or lowering the wafer cassette 28, arespective one of the wafers 52 can be aligned with the slitvalveopening 38 and can be removed from the loadlock chamber 24 through theslitvalve opening 38.

The pump 30 has a low-pressure side 54 and a high-pressure side 56. Anexhaust line 58 has one end that extends into an opening in a base ofthe loadlock chamber 24, and an opposed end connected to thelow-pressure side 54 of the pump 30. The pump 30 can therefore be usedfor pumping a gas from the enclosure 34.

The apparatus 32 includes a source of nitrogen 60, a source of oxygen62, an ozone generator 64, a nitrogen supply valve 68, and an ozonesupply valve 70.

The source of nitrogen 60 is connected to the nitrogen supply valve 68.The nitrogen supply valve 68 is, in turn, connected to a nitrogen supplyline 74. An opposing end of the nitrogen supply line 74 extends into anopening in an upper wall of the loadlock chamber 24. When the valve 68is open, nitrogen gas from the source of nitrogen 60 can therefore besupplied to the enclosure 34. A diffuser (not shown) is located in thenitrogen supply line 74 to reduce the speed of the nitrogen gas.

The source of oxygen 62 may, for example, be substantially pure oxygengas or may be air. It has been found that even filtered air is not asfree of impurities as substantially pure oxygen. The oxygen is typicallyabout 99.999% pure. Substantially pure oxygen may thus be preferred. Theozone generator 64 is connected to the source of oxygen 62.

When oxygen gas from the source of oxygen 62 is supplied to the ozonegenerator the ozone generator 64 generates ozone gas. The ozonegenerator 64 is, in turn, connected to the ozone supply valve 70. Anozone supply line 76 is connected to the ozone supply valve 70. Anopposing end of the ozone supply line 76 extends into an opening in theupper wall of the loadlock chamber 24. When the valve 70 is open, ozonegas generated by the ozone generator 64 can be supplied to the enclosure34. A diffuser (not shown) is located in the ozone supply line 76 toreduce the speed of the ozone gas.

A pressure detector 72 is connected to the exhaust line 58. The pressuredetector 72 can detect the pressure within the exhaust line 58, andtherefore also the pressure within the enclosure 34.

A controller 80 is used for controlling various components of the system10 shown in FIG. 1, including the pump 30, the ozone generator 64, andthe valves 68 and 70 shown in FIG. 2. The controller 80 receives inputfrom the pressure detector 72 and controls all the components based onthe pressure detected by the pressure detector 72 and other variables aswill be described hereinbelow. The controller 80 is typically a computerhaving a processor which is programmed to execute a program whichcontrols all the components of the system 10. The program includesprocessor executable code and is typically stored on a disk or othercomputer readable medium and then loaded into memory of the computerfrom where the processor of the computer reads and executes the programto control the components of the system 10. Particular features of theprogram and how it is constructed will be evident to one skilled in theart from the discussion that follows.

Referring again to FIG. 1, it can be seen that each wafer processingchamber 20A, 20B, or 20C leads directly off the transfer chamber 18. Arespective slitvalve 82A, 82B, and 82C is mounted to open or closecommunication between the transfer chamber 18 and a respective one ofthe wafer processing chambers 20A, 20B or 20C.

The cooldown chamber 22 also leads off the transfer chamber 18 but noslitvalve is provided to open and close communication between thetransfer chamber 18 and the cooldown chamber 22.

A robot 84 is located within the transfer chamber 18. The robot 84 has ablade 86 which, when the robot 84 is operated, can transfer a wafer fromone of the chambers 20, 22, or 24 to another. A susceptor 88 is locatedin each one of the chambers 20 and 22, on which the wafer can be locatedby the blade 86. The slitvalves 82 and the robot 84 are also undercontrol of the controller 80 shown in FIG. 2.

One example of how the controller 80 controls the system 10 is nowdescribed with reference to FIGS. 1 and 2 jointly. FIG. 3 is a flowchart which assists in illustrating how the system 10 is operated.

The slitvalves 42 are initially closed so that the confines of thetransfer chamber 18 are not in communication with the loadlock chambers24. The loadlock chamber 18 is initially evacuated to removecontamination. The loadlock chamber 18 is then backfilled with an inertgas such as nitrogen. The slitvalves 82 are open so that the waferprocessing chambers 20 are in communication with the transfer chamber18. The transfer chamber 18, the wafer processing chamber 20, and thecooldown chamber 22 are filled with an inert gas such as nitrogen gasand are at atmospheric pressure. The door 40 of the first loadlockassembly 14A is open.

A robot (not shown) located within the factory integration unit 12 thenloads a total of twenty-five wafers on the wafer cassette 28 of thefirst loadlock assembly 14A. (Step 1). The door 40 is then closed sothat the wafers 52 are isolated within the loadlock chamber 24. (Step2).

The pump 30 is then switched on so that air passes from the enclosure 34through the exhaust line 58 through the pump 30. (Step 3). The valves68, and 70 are closed so that the enclosure 34 is pumped down to apressure of about 5 Torr.

The pump 30 is then switched off. (Step 4). The valve 68 is then opened.(Step 5). Nitrogen then flows into the enclosure 34 until the pressurewithin the enclosure 34 is substantially the same as the pressure withinthe transfer chamber 18. The valve 68 is then closed. (Step 6).

The slitvalve 42 is then opened. (Step 7). The robot 84 then removesthree wafers consecutively from the wafer cassette 28 and locates onewafer within the first wafer processing chamber 20A, another waferwithin the second wafer processing chamber 20B, and a further waferwithin the third wafer processing chamber 20C. (Step 8). The slitvalves82 are then closed so that the wafer processing chambers 20 are isolatedfrom the transfer chamber 18. (Step 9). An epitaxial silicon layer isthen formed on the wafer in each processing chamber 20. (Step 10). Amixture of gasses is introduced into each one of the wafer processingchambers 20. One of these gasses includes hydrogen. Another one of thegasses is a source of silicon such as silane, dichlorosilane, ortrichlorosilane. The source of silicon reacts with the hydrogen to forman epitaxial layer. Another one of the gasses is typically B₂H₆ whichprovides boron for purposes of doping the epitaxial silicon layer. Heatlamps (not shown) heat the wafers within the wafer processing chambers20 to a temperature of between 600° C. and 1300° C.

Once the formation of the epitaxial silicon layer on one of the wafersis finalized, the processing gasses within the respective chambers 20are replaced by pure hydrogen gas to purge the chambers 20. (Step 11).The respective slitvalve 82 is then opened. (Step 12). The respectivewafer is transferred, utilizing the robot 84, to the cooldown chamber22. (Step 13). Transfer of the wafer takes about twenty seconds. Thewafer remains within the cooldown chamber 22 for about sixty seconds.(Step 14). The robot 84 then transfers the wafer from the cooldownchamber 22 back to the wafer cassette 28. (Step 15). The wafer is thustransferred from the chambers 20 to the wafer cassette 28 without everbeing exposed to oxygen or any other gas that can form an oxide on theepitaxial silicon layer.

The process of forming an expitaxial silicon layer on each wafer iscontinued until all the wafers are processed in a similar manner and allthe wafers are located back on the wafer cassette 28. It takes betweenone and two hours to process twenty-five wafers when forming a 5 micronthick epitaxial silicon layer on each wafer. While the wafers from thefirst loadlock assembly 14A are processed, more wafers can be located onthe wafer cassette 28 of the second loadlock assembly 14B.

Once the wafers are located on the wafer cassette 28 of the firstloadlock assembly 14A, the slitvalve 38 thereof is closed. (Step 16).The wafers 52 are then at a temperature of less than 100° C., but thistemperature can vary depending on the time spent in the cooldown chamber22.

The pump 30 is then again switched on so that nitrogen gas then flowsout of the enclosure 34. (Step 17). The enclosure 34 is pumped down to apressure of about 5 Torr. The pump 30 is then switched off. (Step 18).The ozone generator 64 is then switched on and the valve 70 is opened sothat an ozone gas and oxygen gas mixture flows into the top of theenclosure 34. (Step 19). The ozone gas and oxygen mixture continues toflow into the enclosure 34 until the pressure within the enclosure 34reaches about 600 Torr. The valve 70 is then closed and the ozonegenerator 64 is switched off. (Step 20).

The wafers 52 are then simultaneously exposed to the ozone gas withinthe enclosure 34. Exposure of the epitaxial silicon layer on the wafer52 results in oxidation of the epitaxial silicon layer. The wafers 52are exposed to the ozone gas for a period from one to fifteen minutes.The wafers 52 are simply “soaked” in the ozone gas i.e., there are noadditional sources of excitation which, for example, create a plasma orcreate certain photo effects. An oxide layer forms over the epitaxialsilicon layer of each wafer and has a thickness of about 10 Å to about15 Å, as measured by a multiple wavelength ellipsometry technique, forexposure to ozone gas of about fifteen minutes. The oxide layer thatforms on the wafer is extremely pure because of the controlledconditions to which the wafers 52 are exposed, including the purity ofthe ozone gas and oxygen gas mixture to which the wafers 52 are exposed.

As mentioned previously, hydrogen is used within the wafer processingchamber 20. Hydrogen is highly explosive when mixed with ozone oroxygen. However, for the hydrogen in the processing chambers 20 to mixwith the ozone within the enclosure 34, the system 10 has to failsimultaneously in a number of respects. First, there should be hydrogenwithin one of the wafer processing chambers 20. Second, the hydrogenshould leak past a respective slitvalve 82 of the relevant waferprocessing chamber 20. Leakage of hydrogen past the slitvalve 82 wouldonly occur if the slitvalve 82 does not seal sufficiently on the waferprocessing chamber or when the slitvalve 82 is not closed when hydrogenis introduced into the wafer processing chamber 20. Third, it isrequired that ozone be present within the enclosure 34. Fourth, ozoneshould leak from the enclosure 34 into the transfer chamber 18. Becausethe enclosure 34 is maintained at a pressure below that of the transferchamber 18, it is highly unlikely that there would be any flow of gassesfrom the enclosure 34 into the transfer chamber 18.

Furthermore, it should be noted that the pressure within the enclosure34 never goes over atmospheric pressure so that there is a substantiallyreduced likelihood that ozone gas can escape from the enclosure 34 to asurrounding area and cause exposure of personnel.

It should also be noted that, in the embodiment described, ozone is onlypresent within the apparatus 32 when generated by the ozone generator 64which is only while the enclosure 34 is being filled with ozone. Thereis therefore no contained source of ozone (other than in the loadlockchambers 24) which may leak and cause exposure to personnel or otherreactive gasses. Ozone gas is thus generated at the point of use.

The pump 30 is then again switched on so that the pressure within theenclosure 34 reduces to about 5 Torr. (Step 21). The ozone gas flowingthrough the pump 30 is pumped to a location distant from the system 10,where the ozone gas is neutralized. The ozone gas may for example beneutralized by treatment with a chemical to form oxygen, be scrubbed ina fluidized bed of silica, or be scrubbed in another liquid system.

The valve 68 is then opened so that the enclosure 34 is filled withnitrogen gas. (Step 22). The door 40 is then opened and the wafers 52are transferred from the enclosure 34 into the factory integration unit12. The factory integration unit 12 is filled with air. (Step 23). Theair within the factory integration unit 12 does not form an oxide layeron the epitaxial silicon layer because of the oxide layer which isalready formed thereon due to exposure to ozone.

It takes about twenty-five minutes to process the wafers within thefirst loadlock assembly 14A, as measured from when the slitvalve 42 isclosed until the wafers 52 are removed from the loadlock chamber 24. Thetime taken to process twenty-five wafers by the first loadlock assembly14A is less than the time taken to process twenty-five wafers within thewafer processing chambers 20 and cooling the wafer down in the cooldownchamber 22, because the wafers are processed in batch. As illustrated inFIG. 4 the first loadlock assembly 14A can thus be used in an epitaxialsilicon cycle wherein wafers are transferred to the wafer processingchamber 20 and the cooldown chamber 22. The first loadlock assembly 14Acan then be used in a oxide cycle wherein the wafer is exposed to ozonegas. At the same time when the first loadlock assembly 14A is used foran oxide cycle, the second loadlock assembly 14B can be used for aepitaxial silicon cycle, whereafter the second loadlock assembly 14B canbe used for an oxide cycle. When the second loadlock assembly 14B isused in the oxide cycle, the first loadlock assembly 14A can be used ina epitaxial silicon cycle. It can thus be seen that, because the oxidecycles are shorter than the epitaxial silicon cycles, there is no lapsein time from one epitaxial silicon cycle to a next epitaxial siliconcycle.

FIG. 5 illustrates a wafer 100 which is processed in accordance with theinvention. The wafer includes a monocrystalline substrate 102 on whichan epitaxial silicon layer 104 is formed. A silicon dioxide layer 106 isformed on the epitaxial silicon layer 104. The silicon dioxide layer canlater be removed to leave the expitaxial silicon layer 104 exposed andcontaining substantially no impurities. The silicon dioxide layer can,for example, be removed in a aqueous solution of hydrogen fluoride.

FIG. 6 and FIG. 7 illustrate the ozone generator 64 in more detail. Theozone generator 64 includes a housing 120, two ultraviolet lamps 122,four quartz tubes 124, an inlet pipe 126, and an outlet pipe 128.

The housing 120 is leak tight and dust proof. A mirror 126 is located ona lower surface of the housing 120.

The ultraviolet lamps 122 are located within the housing 120 on a sidethereof opposing the mirror 126. Electrical connectors 128 extend intothe housing 120 to the ultraviolet lamps 122. The ultraviolet lamps 122can be energized by supplying electricity through the cables 128. A leaktight interface exists between the housing 120 and the cables 128 wherethe cables extend into the housing 120.

Each pipe 126 or 128 extends into the housing 120. A leak tightinterface also exists between each pipe 126 or 128 and the housing 120where the pipe 126 or 128 extends into the housing 120. The pipes 126and 128 are located on opposing sides of the housing 120 as can be seenin FIG. 7. The inlet pipe 126 has an inlet opening therein. The pipe 126interconnects ends of the tubes 124 to one another. The pipe 128 extendsthrough ends of the tubes 124 opposing the ends that are interconnectedby the pipe 126. Small openings 130 are formed in the pipe 128 withinthe tubes 124. Each opening 130 is about 2 mm in diameter. The openings130 are located facing away from a flow passage of a gas flowing throughthe tubes 126 so as to avoid a flow channel within each tube 126 and toensure mixing of a gas flowing through each tube 126.

The oxygen source 62 is connected to the inlet tube 126 through aregulator valve 132. The regulator valve 132 can be adjusted so as tocontrol flow to the inlet tube 126.

A nitrogen source 132 is connected to the housing 120. A purge gasoutlet 134 is also provided out of the housing 120.

Nitrogen from the nitrogen source 132 flows through the housing 120 inan area around the tubes 124. The ultraviolet lamps 122 are switched onby providing electricity through the cables 128. Oxygen from the oxygensource 62 flows through the regulator valve 132 and the pipe 126 to thetubes 124. Ultraviolet light is transmitted by the ultraviolet lamps122. The quartz of the tubes 124 is transmissive so that the ultravioletlight enters the tubes 124. One of the ultraviolet lamps is locatedabove two of the tubes 124 and another one of the ultraviolet lamps 122is located above another two of the tubes 124. A substantially equalamount of ultraviolet light enters the tubes 124 because ofsubstantially equal spacing of the lamps 122 over the tubes 124. Moreultraviolet light reflects from the mirror 126 and enters the tubes 124from an opposing side. The ultraviolet light results in a change of someof the oxygen gas within the tubes 124 to ozone gas. A mixture of oxygengas and ozone gas flows around the pipe 128 and leaves the tubes 124through the openings 130, from where the mixture flows through the pipe128 out of the housing 120. While ozone is formed within the tubes 124,the nitrogen in the area around the tubes 124 suppresses ozonegeneration outside of the tubes 124. This reduces exposure of ozone topeople, thereby making the ozone generator 64 safe to operate, andreduces the chance of ozone degradation of components of the ozonegenerator 64 located externally of the tubes 124.

The openings 130 are restrictions in the path of the mixture of oxygenand ozone leaving the tubes 124. Because of the restrictions provided bythe openings 120, free flow of gas through the tubes 124 is restricted.Because of restrictions provided by the openings 120, the gas remainswithin the tubes 124 for longer and the flow thereof is more evenlydistributed between the tubes 124. The residence time of the mixturewithin the tubes 124 is also increased.

FIG. 8 is a graph of ozone generation. A horizontal axis of FIG. 8 isthe rate at which the loadlock chamber is filled in Torr per minute. Thehigher the valve on the horizontal axis, the faster the loadlock chamberwill be filled. A backfill rate of 60 Torr per minute, for example,means that the loadlock chamber is filled to 600 Torr within 10 minutes.The loadlock is preferably filled to 600 Torr within 20 minutes tomaintain throughput, i.e. the rate on the horizontal axis is preferablyat least 30.

A vertical axis of the FIG. 8 graph is ozone concentration in parts permillion. It can be seen from the graph that the ozone concentration ishigher for lower filling rates of the load lock chamber. Furthermore,there is an appreciable increase in ozone concentration for fillingrates below 50 (i.e. a filling time of more than 12 minutes). Thefilling rate is therefore preferably between 20 Torr per minutes and 50Torr per minute for purposes discussed with reference to FIG. 8 alone.

FIG. 9 is a graph of encapsulation of a wafer with an oxide formed withozone gas. A horizontal axis of the FIG. 9 graph is the ozoneconcentration in parts per million and the vertical axis is oxidethickness as measured with a single wavelength ellipsometry technique.The wafer is maintained at about room temperature and is exposed to theair and ozone gas mixture for 12 minutes. There is an increase in oxidethickness with ozone concentration up to an ozone concentration of about400 parts per million. In order to obtain an oxide thickness which issufficiently thick the ozone concentration is preferably at least 250parts per million. From FIG. 9 can thus be gathered that the ozoneconcentration is preferably between 250 parts per million and 350 partsper million. Referring again to FIG. 8, it can be seen that such anozone concentration requires a filling rate of between 33 Torr perminute and 45 Torr per minute. In order to maintain an ozoneconcentration of at least 250 parts per million and an appreciable oxidethickness, the loadlock is preferably filled at a rate of about 45 Torrper minute.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative and not restrictive of the current invention, andthat this invention is not restricted to the specific constructions andarrangements shown and described, since modifications may occur to thoseordinarily skilled in the art. In another embodiment an ozone sourcemay, for example, be a contained source of ozone located externally of aloadlock chamber. In another embodiment, an ozone source such as anozone generator may, for example, be located within a loadlock chamber.

What is claimed:
 1. A method of processing a wafer, which includes: (a)locating a wafer in a wafer processing chamber of a system forprocessing a wafer; (b) forming a silicon layer on the wafer whilelocated in the wafer processing chamber; (c) transferring the wafer fromthe wafer processing chamber to a loadlock chamber of the system whileremaining substantially unexposed to air, the wafer being transferredthrough a slitvalve opening of the loadlock chamber into the loadlockchamber; (d) closing the slitvalve opening; (e) introducing ozone gas inthe loadlock chamber; (f) exposing the wafer to the ozone gas afterbeing transferred from the processing chamber and while located in theloadlock chamber; and (g) removing the wafer from the loadlock chamberout of the system, the wafer being removed through a door opening of theloadlock chamber, the door opening being a different opening than theslitvalve opening.
 2. A method according to claim 1 wherein the systemincludes a transfer chamber leading off the loadlock chamber, and aplurality of wafer processing chambers leading off the transfer chamber,the wafer being transferred from the wafer processing chamber throughthe transfer chamber to the loadlock chamber.
 3. A method according toclaim 1 which includes: (h) loading a plurality of wafers in theloadlock chamber, wherein: step (a) includes transferring a respectivewafer from the loadlock chamber into a respective one of the processingchambers; step (b) includes forming a silicon layer on each one of therespective wafers, wherein a silicon layer is formed on one of thewafers in one of the chambers while a silicon layer is formed on anotherwafer in another one of the chambers; step (c) includes transferring theplurality of wafers to the loadlock chamber; step (d) includes closingthe slitvalve between the loadlock chamber and the transfer chamber;step (f) includes exposing the wafers together to ozone gas whilelocated in the loadlock chamber; and step (g) includes removing theplurality of wafers from the loadlock chamber out of the system.
 4. Amethod according to claim 3 wherein the time taken from when step (a) isstarted until step (d) is completed is at least twice as long as thetime from when step (d) is completed until step (g) is completed.
 5. Amethod according to claim 3 wherein the loadlock chamber is a firstloadlock chamber and the plurality of wafers is a first plurality ofwafers, the method including: (i) locating a second plurality of wafersin a second loadlock chamber; (j) transferring a respective wafer fromthe second loadlock chamber into a respective one of the processingchambers; (k) forming a silicon layer on each one of the wafers of thesecond plurality of wafers located in one of the chambers; (l)transferring the second plurality of wafers to the second loadlockchamber; (m) closing off communication between the second loadlockchamber and the transfer chamber; (n) exposing the second plurality ofwafers together to ozone gas while located in the second loadlockchamber; and (o) removing the second plurality of wafers from the secondloadlock chamber out of the system.
 6. A method according to claim 5wherein steps (d), (f) and (g) are carried out entirely within a timeperiod from when step (j) is started until step (m) is completed.
 7. Amethod according to claim 5 wherein, when step (f) is carried out, thepressure within the first loadlock chamber is below the pressure in thetransfer chamber.
 8. A method according to claim 2 wherein the pressurewithin the loadlock chamber remains below the pressure within thetransfer chamber while the wafer is exposed to the ozone gas.
 9. Amethod according to claim 1 wherein the system includes a cooldownchamber, the wafer being transferred from the wafer processing chamberto the cooldown chamber and from the cooldown chamber to the loadlockchamber.
 10. A method according to claim 1 wherein a plurality ofwafers, each having a silicon layer formed thereon, are located in theloadlock chamber and the plurality of wafers are simultaneously exposedto the ozone gas.
 11. A method according to claim 1 which includesintroducing the ozone gas from outside the loadlock chamber into theloadlock chamber.
 12. A method according to claim 1 which includesgenerating the ozone gas.
 13. A method of processing a wafer, whichincludes: (a) locating a wafer in a wafer processing chamber of a systemfrom processing a wafer; (b) forming a silicon layer on the wafer whilelocated in the wafer processing chamber; (c) transferring the waferprocessing chamber to a loadlock chamber of the system while remainingsubstantially unexposed to air, the wafer being transferred through aslitvalve opening of the loadlock chamber into the loadlock chamber; (d)closing the slitvalve opening; (e) introducing ozone gas in the loadlockchamber; (f) exposing the wafer to the ozone gas after being transferredfrom the processing chamber and while located in the loadlock chamber;(g) removing ozone from the loadlock chamber, the pressure in theloadlock chamber during (f) and (g) remaining below the pressure in theprocessing chamber; and (h) removing the wafer from the loadlock chamberout of the system, the wafer being removed through a door opening of theloadlock chamber, the door opening being a different opening than theslitvalve opening.
 14. A method according to claim 13 wherein hydrogengas is present within the processing chamber of any given time betweenwhen (g) is started and (h) ends.
 15. A method according to claim 13wherein the pressure within the loadlock chamber remains belowatmospheric pressure during (f) and (g).
 16. A method according to claim1 wherein substantially no oxide layer forms on the silicon layer beforeexposure to the ozone gas.